Sheet for Structural Material Core, Core and Structural Material Comprising Such a Sheet

ABSTRACT

Sheet for core of structural material sandwich extending substantially along an extension plane and having an upper surface and a lower surface which are opposite along a thickness direction, where the sheet is provided with a plurality of upper and lower surfaces for bonding near the upper and lower surfaces thereof, where the sheet comprises a three-dimensional network of edges separated by connecting surfaces, where each edge is defined by a nonplanar profiled wall delimited by an upper bonding surface, a lower bonding surface and two parallel straight lines connecting said upper and lower bonding surfaces by following an edge direction, and where each connecting surface is delimited by at least three edges.

The present invention relates to a sheet for structural material core, a core for structural material comprising such a sheet and a structural material sandwich comprising such a core.

Structural material sandwiches are generally composed of two external skins rigidly connected to opposite surfaces of a core. Said core can be produced of a wide variety of constitutive materials and is made such that it has a high structural strength against compression and flexion while keeping a minimal weight. These structural materials have many applications, for example in the aeronautic or automobile field.

The invention more specifically relates to a structural material sandwich core sheet extending substantially along an extension plane and having an upper surface and a lower surface which are opposite along a thickness direction perpendicular to the extension plane, where the sheet is provided with a plurality of upper surfaces for bonding near the upper surface thereof and also a plurality of lower surfaces for bonding near the lower surface thereof.

The document U.S. Pat. No. 4,495,237 describes an example of a structural material sandwich core sheet comprising an arrangement of truncated pyramids with chamfered edges separated by empty channels. A structural material sandwich core can be formed by stacking two such sheets in staggered rows, where one is turned over relative to the other such that the truncated surfaces of the pyramids of each of said sheets come into contact with the hollows separating the truncated pyramids of the other sheet.

The present invention especially has an object of proposing a core sheet, a core structure and a structural material sandwich having a smaller weight and improved strength properties and constituting a viable economic alternative to known solutions.

For this purpose, according to the invention, the structural material sandwich core sheet in question is characterized in that it includes a three dimensional network of edges (separated by connecting surfaces,

in that each edge is defined by a non-planar profiled wall delimited by

one upper bonding surface among the plurality of upper bonding surfaces

one lower bonding surface among the plurality of lower bonding surfaces, and

two substantially parallel straight lines connecting said upper bonding surface to said lower bonding surface by following an edge direction,

and in that each connecting surface is delimited by at least three edges.

Because of these arrangements, the structural material core sheet according to the invention has good mechanical properties while having a reduced weight. In fact, each of the edges is defined by a nonplanar profiled wall and thus has significant compressional rigidity along the edge direction thereof. Since the network of edges is three-dimensional, the mechanical strength of the structure is therefore significant along all spatial directions. A structural material core and a material using said sheets therefore have a very good ratio between mechanical strength and weight, and thus a significant rigidity both for flexion and compression. A structural material core using said sheets has very good properties as an energy absorber, for example during impacts. A structural material core using said sheets also has an improved shearing behavior. By using a single sheet (foldable or not), especially for cores whose density is below 100 kg/m³, fabric can be used for construction thereof because of a greater thickness with which a composite material core can be made.

For example, a 20 mm thick sheet could weigh 1 kg/m² for a final volume density of the material of 50 kg/m³. In plastics processing, a sheet about 1 mm thick before thermoforming could be used, and for composites (where the ratio between the expanded surface and the projected surface is for example less than three) by considering an average volume density of 1590 kg/m³ for carbon/epoxy, the thickness of the sheet could be over 0.2 mm, for about two composite plies for producing such a sheet.

In various embodiments of the core sheet according to the invention, use could furthermore be made of one and/or the other of the following arrangements

According to an aspect of the invention, the upper and lower bonding surfaces are distributed periodically.

According to an aspect of the invention, the plurality of upper bonding surfaces and the plurality of lower bonding surfaces are arranged staggered in rows in the extension plane.

According to an aspect of the invention, each connecting surface is delimited by at least four edges, two lower bonding surfaces and two upper bonding surfaces.

According to an aspect of the invention, the connecting surfaces have a barycenter substantially located in the area of the median plane parallel to the extension plane of the sheet and located at the middle of a thickness distance separating the upper and lower surfaces, where said distance is considered along the thickness direction.

According to an aspect of the invention, the connecting surfaces are minimal surfaces.

According to an aspect of the invention, the connecting surfaces are minimal surfaces which are segmented or provided with grooves.

According to an aspect of the invention, the upper and lower bonding surfaces are identical.

According to an aspect of the invention, for at least one edge, the two parallel straight lines delimiting said edge are not coincident.

According to an aspect of the invention, each nonplanar profiled wall of edges is constituted uniquely of straight lines connecting said upper bonding surface delimiting it to said lower bonding surface delimiting it.

The invention also relates to a sandwich structural material core comprising at least one sheet as defined above.

The invention also relates to a sandwich structural material core comprising a core as defined above.

Other features and advantages of the invention will become apparent during the following description of several embodiments thereof, given as nonlimiting examples, with reference to the attached drawings.

In the drawings:

FIG. 1 is a perspective view of a structural material sandwich core sheet according to a first embodiment.

FIG. 2 is a top view of the sheet from FIG. 1.

FIGS. 3 a and 3 b are perspective views of structural material sandwich core sheets according to two other embodiments.

FIG. 4 is a perspective view of a structural material sandwich core sheet according to another embodiment.

FIGS. 5 a and 5 b correspond to the sections VA and VB indicated on FIG. 4 and show the conformation of the nonplanar profiled walls of the edges at different positions along the directions of the edges.

FIG. 6 is a perspective view of a structural material sandwich core sheet according to another embodiment.

FIGS. 7 a and 7 b correspond to the sections VIIA and VIIB indicated on FIG. 6 and show the conformation of the nonplanar profiled walls of the edges at different positions along the directions of the edges.

FIG. 8 a is a perspective view of a structural material sandwich according to an embodiment of the invention.

FIG. 8 b is a front view of the structural material sandwich from FIG. 8 a.

In the various figures, the same references designate identical or similar items.

FIGS. 1 and 2 show a structural material sandwich core sheet 1 according to a first embodiment of the present invention. This sheet 1 extends along extension directions X and Y and has an upper surface 2 and also a lower surface 3 located on opposite sides of a median plane 99.

The upper 2 and lower 3 surfaces are opposite along a thickness direction Z, perpendicular to the plane of extension formed by the extension directions X and Y.

The upper and lower surfaces can be parallel to each other and also to the median plane 99.

The upper 2 and lower 3 surfaces are separated by a nonzero thickness distance, measured along the thickness direction Z.

The upper 2 and lower 3 surfaces are thus distinct.

The median plane 99 is located at half of the thickness distance separating the upper 2 and lower 3 surfaces.

Around the upper surface 2 thereof, the sheet 1 has a plurality of upper bonding surfaces 2 a.

Around the lower surface 3 thereof, the sheet 1 has a plurality of lower bonding surfaces 3 a,

The upper bonding surfaces 2 a can be distributed periodically, so as to form a periodic network, for example a square network as shown in FIGS. 1 and 2.

Identically, the lower bonding surfaces 3 a can be distributed periodically, so as to form a periodic network, for example a square network as shown in FIGS. 1 and 2.

The periodic networks formed by the upper 2 a and lower 3 a bonding surfaces can be arranged in staggered rows, with an upper bonding surface being surrounded by lower bonding surfaces and vice versa.

The upper and lower bonding surfaces can for example be planar and have any shape at all.

They can be perforated or solid.

As a variant, the upper and lower bonding surfaces can have recessed or projecting parts according to the thickness direction Z.

The upper bonding surfaces 2 a can be identical to each other.

Similarly, the lower bonding surfaces 3 a can be identical to each other.

The upper bonding surfaces 2 a and the lower bonding surfaces 3 a can be identical to each other, as described previously in relation to FIGS. 4, 5 a, 5 b, 6, 7 a and 7 b.

This can for example serve to provide an identical adhesive behavior of the sheet with external skins 200 for one structural material sandwich core 100 such as for example FIGS. 8 a and 8 b show and detailed before.

Other networks and also other shapes for the upper and lower bonding surfaces than the network and surfaces shown in FIGS. 1 and 2 and described above can be considered as indicated above can be considered as indicated later.

Sheet 1 can be made of a material like a plastic, metal, alloy, composite material or resin. The thickness of the material making up sheet 1 can range from 8 μm to 2 mm.

As indicated in FIGS. 1 and 2, the sheet 1 furthermore comprises a three-dimensional network of edges 4 separated by connecting surfaces 5.

The edges 4 are each defined by a nonplanar profiled wall 5 delimited by an upper bonding surface, a lower bonding surface and two parallel straight lines 6 connecting said upper bonding surface to said lower bonding surface by following an edge direction 7.

Three-dimensional network of edges is understood to mean that the set of edges 4 includes at least three edges 4 for which the edge directions 7 are not coplanar.

The upper end 4 a of each edge 4 is thus made up by an upper bonding surface 2 a and the lower end 4 b by a lower bonding surface 3 a.

The parallel straight lines 6 are each connected at one of their ends to an upper bonding surface 2 a and at their other end to a lower bonding surface 3 a.

In an alternative embodiment, the parallel straight lines 6 can be substantially parallel meaning for example, slightly curved or slightly inclined relative to each other.

In the embodiment from FIGS. 1 and 2, the profiled nonplanar wall 5 of the edges 4 has the shape of a half-cylinder cut along one of the planes of extension thereof.

Other shapes for the nonplanar profiled walls 5 of the edges 4 can be conceived as detailed below.

Thus in particular, the nonplanar profiled walls 5 of the edges 4 can be recessed, projecting or comprise both recessed parts and projecting parts.

Advantageously, the nonplanar profiled walls 5 are made up uniquely of straight lines connecting the upper bonding surfaces 2 a delimiting them to the lower bonding surface 3 a delimiting them. This makes it possible to further increase the mechanical strength of the structure.

Connecting surfaces 8 connect the edges 4 to each other and with the lower 3 a and upper 2 a bonding surfaces.

The connecting surfaces 8 are advantageously delimited by at least three edges 4. Thus, the connecting surfaces have a minimal weight.

In the embodiment from FIGS. 1 and 2, the connecting surfaces 8 are each delimited by two upper bonding surfaces 2 a, two lower bonding surfaces 3 a and four edges 4, where said edges each connect one of said two upper bonding surfaces to one of said two lower bonding surfaces.

The connecting surfaces 8 are advantageously minimal surfaces, meaning that each of them has a minimal area while connecting all the elements which delimit them. This makes it possible to even further reduce the weight of the sheet while keeping good mechanical properties.

Thus, the connecting surfaces 8 can have a saddle profile also called hyperbolic paraboloid, meaning that they have a negative curvature.

Furthermore, the barycenter 8 b of each connecting surface 8 can advantageously be located near the median plane 99 parallel to the XY extension plane of sheet 1 and located half of the distance in thickness separating the upper 2 and lower 3 surfaces.

The connecting surfaces 8 can have grooves 8 a, for example profiled grooves as shown in FIGS. 1 and 2.

As shown in FIGS. 3 a and 3 b, the connecting surfaces 8 can also be segmented, meaning made up of planar facets. In this embodiment, the connecting surfaces 8 no longer constitute minimal surfaces but constitute a segmented approximation thereof.

The connecting surfaces 8 can finally be solid or perforated with openings in order to further lighten the structure.

In particular, all or only part of the connecting surfaces 8 can be perforated with openings.

Each opening can be made on an associated connecting surface. Associated connecting surface is understood to mean the connecting surface in which the opening in question is made.

In a possible implementation, each opening can be made on only a part of the associated connecting surface. Said part can in particular include the barycenter of the associated connecting surface.

Said part can in particular extend over a portion of the associated connecting surface whose area is less than half the area of the associated connecting surface.

In another possible implementation, each opening can be made over the majority or the entirety of the associated connecting surface, in particular, each opening can extend over a portion of the associated connecting surface whose area is greater than half the area of the associated connecting surface, and in particular greater than three quarters of the area of the associated connecting surface.

With reference to FIGS. 4, 5 a and 5 b, the nonplanar profiled walls 5 of the edges 4 can have an “inclined sinusoidal” shape.

Thus, a nonplanar profiled wall 5 of an edge 4 can have an upper profile 5 a near the upper bonding surface delimiting it, for example a recessed circular arc profile as shown in FIG. 4.

The nonplanar profiled wall 5 can have a lower profile 5 b near the lower bonding surface delimiting it, for example a projecting circular arc profile as shown in FIG. 4.

The upper 2 a and lower 3 a bonding surfaces can thus be identical.

This can for example serve to provide an identical adhesive behavior of the sheet with external skins 200 for a structural material sandwich core 100 such as for example FIGS. 8 a and 8 b show and detailed before.

Between the upper profile 5 a and the lower profile 5 b, the nonplanar profiled wall 5 can have a shaped profile of projecting parts 5 c and recessed parts 5 d progressively offset along the edge direction 7 from the side of one of the parallel straight lines 6 as shown on the FIGS. 5 a and 5 b.

Thus, the nonplanar profiled walls 5 can in particular comprise at least one inclined straight line 5 e, inclined relative to the edge direction 7 and substantially or exactly connecting the upper end 6 a of one of the two parallel straight lines 6 to the lower end 6 b of the other of the two parallel straight lines 6 delimiting the edge 4.

As shown in FIGS. 4 and 5A, the inclined straight line 5 e can connect for example a first point 6 c of the upper bonding surface 2 a and a second point 6 d of the lower bonding surface 3 a, where the first point 6 c is near the upper end 6 a and the second point 6 d is near the lower end 6 b.

Said upper 6 a and lower 6 b ends of said straight lines 6 are understood to be the intersections of said parallel straight lines 6 and respectively the upper bonding surface 2 a and the lower bonding surface 3 a delimiting the edge 4.

In this embodiment, the edges 4 are additionally joined at their upper ends 4 a and lower ends 4 b, meaning that the upper ends 6 a of two parallel straight lines 6 respectively delimiting two edges 4 which are distinct and connected to a single upper bonding surface 2 a are merged.

Identically, the lower ends 6 b of two parallel straight lines 6 respectively delimiting two distinct edges 4 and connected to a single lower bonding surface 3 a are merged.

The periphery of the upper and lower bonding surfaces is then constituted uniquely by respectively upper 4 a and lower 4 b ends of edges 4.

In this embodiment, each edge 4 thus has a self-bracing made by the inclined straight lines 5 e and the adjacent edges 4.

As a variant, the profile of the nonplanar profiled wall 5 can be more complex and said profiled wall can have upper 5 a and lower 5 b profiles having several recessed parts as shown in FIGS. 6, 7 a and 7 b.

With reference to FIGS. 8 a and 8 b, a sandwich structural material core 100 can be made by assembling two sheets 1, along the thickness direction Z of said sheets 1, for example respectively near the upper 2 a and lower 3 a bonding surfaces of said sheets 1.

As a variant, other sheets 1 can be attached identically to said assembly of two sheets 1 so as to form a sandwich structural material core 100 of arbitrary thickness.

Finally, still with reference to FIGS. 8 a and 8 b, a sandwich structural material 1000 can be obtained by superimposing, on at least one of the upper or lower surfaces of a core 100, an outer skin 200, for example an upper outer skin 200 and a lower outer skin 300. Said skins are for example formed of a fiber reinforced plastic composite material.

It is also possible to insert skins 200 between one or more sheets constituting a sandwich structural material core 100, which serves for example to increase the mechanical strength of said core 100. 

1. As structural material sandwich core sheet extending substantially along an extension plane and having an upper surface and a lower surface which are opposite along a thickness direction perpendicular to the extension plane, where the sheet is provided with a plurality of upper surfaces for bonding near the upper surface thereof and also a plurality of lower surfaces for bonding near the lower surface thereof, the sheet wherein it includes a three dimensional network of edges separated by connecting surfaces, in that each edge is defined by a non-planar profiled wall delimited by one upper bonding surface among the plurality of upper bonding surfaces one lower bonding surface among the plurality of lower bonding surfaces, and two substantially parallel straight lines connecting said upper bonding surface to said lower bonding surface by following an edge direction, and in that each connecting surface is delimited by at least three edges and has a barycenter substantially located in the area of the median plane parallel to the extension plane of the sheet and located at the middle of a thickness distance separating the upper and lower surfaces, where said distance is considered along the thickness direction.
 2. The sheet according to claim 1, wherein the upper and lower bonding surfaces are distributed periodically.
 3. The sheet according to claim 1, wherein the plurality of upper bonding surfaces and the plurality of lower bonding surfaces are arranged staggered in rows in the extension plane.
 4. The sheet according to claim 1, wherein each connecting surface is delimited by at least four edges, two lower bonding surfaces and two upper bonding surfaces.
 5. The sheet according to claim 1, wherein the connecting surfaces are minimal surfaces.
 6. The sheet according to claim 1, wherein the connecting surfaces are minimal surfaces which are segmented or provided with grooves.
 7. The sheet according to claim 1, wherein the connecting surfaces are perforated with openings.
 8. The sheet according to claim 1, wherein the upper and lower bonding surfaces are identical.
 9. The sheet according to claim 1, wherein for at least one edge, the two parallel straight lines delimiting said edge are not coincident.
 10. The sheet according to claim 1, wherein each nonplanar profiled wall of edges is constituted uniquely of straight lines connecting said upper bonding surface delimiting it to said lower bonding surface delimiting it.
 11. A core for structural materials sandwich comprising at least one sheet according to claim
 1. 12. A structural material sandwich comprising a core according to claim
 11. 